She must poo within 12 hours or you have to contact your vet. It’s normal for anesthetics to cause the intestine to slow down, but it must “speed up” again after the surgery.
It’s great that she has eaten. Try to get her to eat more. You can mix baby fruit puree with soaked pellets if she’s not eating her pellets. If you have CC you can give that. Any treat she wants she should get (in moderate amounts of course- but if she tries to devour treats and beg for more, you can consider the crisis pretty much over).
It’s really important that you keep her warm. Rabbits tend to become hypothermic after surgery. Low body temp slow things down further and it becomes a vicious cycle.
Thickening of the uterus means the cells in the the uterine lining are multiplying more than they should, so the uterine wall becomes thicker. It’s driven by estrogen. It’s not cancer, but it can become cancer. So it’s really great that you had her spayed!